1. Field of the Invention
The present invention relates to an apparatus for punching holes into sheet materials, and more particularly, relates to a high speed punching apparatus of the so-called bullet punch type for the sequential punching of holes into an advancing web or sheet of paper, plastic or other film material through the intermediary of a high-speed projectile reciprocatively piercing through the material.
In the production of various kinds of articles which are constituted from either sheets of paper, paperboard or plastic film webs, there is frequently a need to punch a plurality of accurately located holes in the material. Quite often, in mass-production technologies, the sheet or web of film material is advanced at relatively high speeds so as to necessitate the employment use of rapidly operating, and generally highly sophisticated hole punching equipment for accurately correlating the hole punching sequences with the advance of the sheet or film material. More recently, advances in production techniques have necessitated the use of hole punching apparatus which must operate at ever higher punching speeds, while maintaining a tenable degree of precision, resulting in the need for frequent replacements of the cutting implements or knives of the hole punches due to dulling or wear by new or resharpened knives or cutting implements. This requirement is not only expensive from the viewpoint of having constantly supply new or replacement knives or cutting implements, but also necessitates considerable expenditure of labor and "downtime" for servicing the entire production facility, resulting in appreciable financial expenditures which frequently renders the operation less economical.
2. Discussion of the Prior Art
Heretofore, the major types of hole punching systems and methods employed in industry for the punching of holes into sheets or film web materials were, in one instance, of the so-called ball punch type, providing for a stationary ball and a cooperating movable knife which strikes against a film as the latter is conveyed between the ball and knife, so as to form a cutout or hole in the film. This results in the rapid wear of the cutting surfaces or edges of the knife, and as a consequence necessitating the frequent replacement of the knife. Another hole punching system contemplates the use of a rotating knife which essentially drills through the film or sheet material, thereby also causing the extremely rapid wear of the cutting edges of the knife. A further arrangement provides for a punch, or knife, which is received within a complementary die and then returned to its initial set position subsequent to punching the hole in the material. Another system, which is similar to the above-mentioned punching die, provides for a knife in the form of a hollow serrated tube having a cutting edge piercing the film material and then engaging into an opening provided in a die. Finally, still another system employed in industry provides for a so-called shearing of the material, in which the holes in the sheet for film web are punched out by either a knife passing over the film while cutting the latter, or in which a knife is embedded in a grooved roll and the film web is cut when it is conveyed between the bed for the knife which is formed in the surface of the roll and the cutting edge of the knife. Practically all presently employed hole punching systems are, to a greater or lesser extent, based on the above-mentioned concepts.
In all of the aforementioned hole punching systems, in addition to the necessity for providing rather complex and expensive apparatus, the advancing web must be stopped during the punching sequence in order to be able to allow for the formation of accurately sized holes in the material. This not only slows down the advance of the film web or sheet material, but also requires complex devices for synchronizing the resultingly intermittent advance of the film web with the punching of the holes by the hole punching apparatus.
Consequently, in order to considerably reduce the wear on the cutting edge of the knife or punch which is employed in forming the holes in the sheet or film web material, there has more recently been developed the concept of a so-called "bullet punch", in which a projectile-shaped cutting body possessing cutting edges or knives at opposite ends thereof, is propelled at high speeds between two end positions on opposite surfaces of an advancing film web or sheet being passed between the positions, and in which the knives pierce through the film web as the projectile is propelled therethrough so as to cause the opposite knife edges to alternatingly form sequential holes in the advancing sheet or film web material. This will clearly result in a reduced wear of the knife edges while allowing for a rapid advance of the sheet or film web in a practically continuous manner.
Carr U.S. Pat. No. 3,156,148 discloses a data processing card punching apparatus and hole punching method, in which a closed loop-shaped conduit is connected to a source of pressurized air, and incorporates a conduit section having a gap cut transversely therethrough for the passage of data processing cards across the conduit section. A projectile having cutting blades at each end thereof adapted to punch holes through the cards is reciprocated within the conduit section in response to pressurized air being alternatingly applied to opposite ends of the projectile, thereby causing the latter to be propelled from one end of the conduit section towards the other end, and back again. This will cause the projectile, during each displacement thereof, to pierce data processing cards sequentially interposed in the gap formed in the conduit section, and with material chips punched out of the data cards by the projectile to drop out through suitable apertures formed in the conduit section. Although this particular structure allows for a higher operating speed during the punching of holes in sequentially advanced data processing cards, while reducing wear on the cutting blades, quite frequently punched out card chips will tend to clog up within the conduit section. Moreover, there is no accurate control over the advancing speed and reciprocating motion of the projectile, thereby rendering the entire operation somewhat inaccurate and uneconomical for use with continuously advancing webs of material.
Bohl, et al. U.S. Pat. No. 2,924,147 discloses a blast-free explosive line cutter in which a projectile is adapted to pierce through a rod member extending through a conduit so as to separate the rod member into separate rod sections. This patent does not disclose the concept of employing a reciprocating projectile or bullet punch employed in the punching of holes into a continuously advancing sheet or web of a film material.
Lagain U.S. Pat. No. 3,779,121 discloses a sheet metal cutting apparatus in which a projectile is adapted to be reciprocated back and forth within a tubular section under the action of fluid pressure alternatively applied to opposite ends of the projectile, and which includes an external cutting member adapted to slice through sheet members disposed therebeneath, in which opposite cutting edges thereon will alternatingly cut through sheet members as the cutting member reciprocates in conjunction with the movement of the projectile. This structure does not provide for the highly accurate bullet punch arrangement as contemplated by the present invention.